The transparent touch-panel type coordinate input device is attached to the front of the display face of a display device such as a CRT, LCD (liquid-crystal display), etc. and generates several controls in response to a simple push above the display face by an operator seeing the same. Thus, because it is adapted for simple input in so-called menue systems, there are advantages in employing it as an input device for the computer.
For the touch-panel input device there have been proposed several systems such as the resistance film system, capacity system, acoustic system utilizing surface elastic waves, and photoelectric system utilizing an optical beam. Among them, the photoelectric system utilizes photoelectric elements stored around the margin of the display face, so that there is little danger of a user coming into touch with the photoelectric elements, and there is no fear of an input panel receiving scratches or being damaged by adhesion of liquid because such an input panel does not exist on the front of the display face different from the other systems, and its operation reliability is high, accordingly, it is said that this photoelectric system has bright prospects for the future.
One such photoelectric system, uses a light emitting diode (hereinafter referred to as LED) as a light emitting element; a number of paired light emitting elements and light receiving elements are arranged for X, Y coordinates; and the light emitting elements of respective coordinates are driven in sequence one after another to scan over the display face by means of a ray. It has such advantages as that its cost is low as compared with a system employing a laser beam, and its lifetime is long because the photoelectric element is one of the solid-state parts.
However, the conventional touch-panel input device of the photoelectric system must continuously scan the display face by means of the ray at high speed, therefore, its consumption power is pulling up, a careless movement of a finger tip onto the display face causes an input corresponding to the spot where the finger tip approaches, further even a point on the display face on which an insect etc. is settling is also input, and, accordingly, misinputting can easily be caused by careless handling or unexpected events. Further, when the finger tip is trembling or fine coordinate values are to be directed, erroneous input occurs easily through inputting of adjacent coordinate values, thus, this frequently requires a direction-canceling operation and a retry. Furthermore, in case where the display device is a CRT, the display face is curved and this is apt to produce a parallax, whereby erroneous input would occur more frequently. Still more, in the case of successive inputting, the finger tip etc. having directed a first set of input coordinate values must be pulled away from the display face (from the plane being scanned by means of the ray) and then must be floated to re-enter at a next input coordinate spot while aiming at that spot, this is very different from the resistance film system etc. where the finger tip slides on the display face (sheet) without detaching therefrom and pushes a desired spot to achieve an input operation.